We are using your PRO2PDF plugin here at https://knospe-aba.com/.
We also use Formidable Form Pro.
The mails with the PDFs to the customers and on the website are generated and sent by mail or displayed on the website.
You can test the form, but I would not publish the link.
The PDFs to the website owner only arrive broken at 0 KB.
Do you have any idea what might be causing this?